The present invention relates to a superconductive tube for magnetic shielding as well as to a method for manufacturing such a superconductive tube.
Ferromagnetic materials such as permalloy or ferrite have been utilized to shield the space surrounded by them. Recently, many devices have been introduced to shield the magnetic field by the Meissner effect exerted by superconductors. For example, in Japanese Patent Laid Open No. 1-134998 (1989) superconductive materials were arranged to the innermost side of the space in which the magnetic field is shielded. In U.S. patent application Ser. No. 509,438 a tube for magnetic shielding, i.e., shielding a magnetic field, has been proposed by the present applicants that comprises at least two layers which include a layer of a substrate and a layer of superconductor arranged in this order from the magnetic source to be shielded.
However, a tube for magnetic shielding using an oxide superconductor that can be used in actual practice has remained in a developing stage at present. When superconductive materials are merely combined, a magnetic field is known to leak through the joints, and high performance in shielding a magnetic field cannot be achieved. This makes it necessary to form a structure of superconductive materials in an integral form. However, as the structure of superconductive materials become larger, it becomes more difficult to integrally form a structure of superconductive materials; it is not industrially preferable that the apparatus for manufacturing them becomes larger.
On the other hand, for a large-size tube for magnetic shielding it is required to use a metal or other robust material as a substrate to keep the mechanical strength of the tube. When a layer of oxide superconductor forms on a metal substrate, there remains a problem that the metal in the substrate reacts with the oxide superconductor; this problem is especially aggravated with compounds belonging to a Bi-Sr-Ca-Cu-O system. To solve this problem it is customary to include an intermediate medium with a noble metal between the substrate and layer of oxide superconductor to prevent the reaction.
However, this solution poses another problem. It is difficult to form the intermediate medium uniformly over a large-size metal substrate, and more difficult to form a layer of oxide superconductor uniformly on the intermediate medium. As a result satisfactory superconductive properties cannot be obtained.